Trenchless installation techniques are known for underground placement of utility and transmission lines, such as for oil and gas products, electrical power, and telecommunications. One method of trenchless installation is referred to as “horizontal directional drilling”, a method preferred for placing pipelines under obstacles such as rivers or lakes. Variations of this method are disclosed and taught by my prior patents, entitled “Drilling Method and Apparatus for Large Diameter Pipe”, U.S. Pat. No. 4,221,503; and “Method and Apparatus for Thrusting a Pipeline into Bore Hole”, U.S. Pat. No. 5,375,945.
A known method of horizontal directional drilling includes drilling a borehole with a drilling rig and drilling pipe string, and then pulling a pipeline back through the borehole. The borehole extends in the desired path for the pipeline, such as under a river or lake. After the borehole has been drilled by the drill string, the front end of the pipeline is attached to the drill string so that the pipeline is pulled into the borehole as the drill string is removed. The drilling rig located at the first end of the borehole (the borehole entry) may be used to withdraw the drill string from the borehole, and in addition, a pipe thruster located at the second end of the borehole (the borehole exit) may be used to push the pipeline into the borehole. If the pipeline is small and short enough, the drilling rig alone may be used to withdraw the drill string and pull the pipeline into the borehole, or the pipe thruster alone may be used to push the pipeline into the borehole. For larger or longer pipes, the drilling rig and the pipe thruster work together to install the pipeline into the borehole.
Various known pipe thrusters and associated methods for placing pipelines into boreholes have encountered shortcomings that limit their effectiveness and performance. As an example, there have been difficulties in arranging a pipe thruster that can easily and quickly reverse direction, to withdraw a pipeline from a borehole if necessary. This may be useful, for example, if the pipeline gets stuck in the borehole or becomes damaged during installation, or if the borehole needs reconditioning. Existing pipe thrusters may need to be partially disassembled and reconfigured to move in reverse, and/or may operate more slowly in reverse. This has proven to be time consuming and costly, and the inability to quickly withdraw the pipeline from the borehole raises the risk of the pipeline becoming stuck.
Another example is the difficulty of coordinating the movement of the pipe thruster on one end and the drilling rig on the other end. Some pipe thrusters operate through a shorter travel range than the drilling rig, and as a result the drilling rig must pause mid-stroke to wait for the pipe thruster to reset. When hydraulic cylinders are used to thrust the pipeline, short hydraulic cylinders may have to be repeatedly extended and retracted, slowing down the overall operation, while longer hydraulic cylinders may be subject to damage from excessive compression and/or torsional damage from pipeline roll.
During installation, stabilization of the pipeline against torsion and roll has also proved challenging. In addition, existing pipe thrusters have limited features and are difficult to operate. Accordingly a need exists for an improved pipe thruster that is easier to operate, with a more robust design.